1Dead battery&two trucks running?

Discussion in 'Mechanic and Repair' started by SLR, Apr 19, 2007.

  1. SLR

    SLR LawnSite Gold Member
    Posts: 3,218

    Ok so my brother-in laws 06 dodges battery was completely dead,we boost it to life with my truck,after it starts he says to leave it charge ,having both running and charging his..Question of the day: Could this have dire consequences on an electrical system/altenator? If my truck is putting out 14.4 amps+ his putting out 14.4,what kind of damage was i risking, if any.Seems a bit much for my battery to be getting over 28 volts during his recharging for ten minutes,not to mention the combined output of altenator amps.
     
  2. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    What you were actually seeing is 14.4 Volts, The voltage regulator senses how much voltage thats needed to keep the battery up and does not exceed the 15 VDC limit as long as it's working correctly no matter how many batteries or alternators are in the system.

    The problem with jumping another vehicle off is if the other vehicle has a dead/low battery due to a non working alternator (possible internal short) and your vehicle is running when they hit the key it could blow your alternator also.

    Always pre-charge another vehicle for a few minutes then turn yours off before the other person tries to start theirs.

    Alternators are no longer cheap.....
     
  3. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

    Save YOUR gas!
    With both alternators charging his battery, it may be more current than his battery can safely handle. Blow it up and you both may be buying new charging systems!
    IF his battery is good, 15 minutes of "his" charging should be sufficient. If it's bad, you've both wasted gas for nothing, plus the risk.
     
  4. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    Bill,

    I don't believe leaving cables on would blow the battery up.
    Both voltage regulators would sense more voltage than needed and drop the output.
     
  5. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

    Rob, I don't really disagree, but-
    If the battery was totally dead or defective, it may draw enough load that both alternators could try to charge at the maximum rate.

    When someone has a "dead" battery, I tend to wonder why on an alternator equipped vehicle. Usually, it's because it's simply old, but.....
     
  6. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    Hmmm, I see what your saying Bill.....[​IMG]
     
  7. dmc337

    dmc337 LawnSite Member
    Posts: 49

    This winter I had to work in a starter and alternator shop. You will need to put the 'dead' battery on a charger for a little while to slow charge it back up to full capacity. Fast charging with the alternator may blow a voltage regulator.
     
  8. SLR

    SLR LawnSite Gold Member
    Posts: 3,218

    I think the best input,that i shall thus far live by, is Restrorobs:

    "Always pre-charge another vehicle for a few minutes then turn yours off before the other person tries to start theirs".

    That is by far the safest,why didn't i think of doing that.Curiously my battery is now a dead duck! :(

    Thanks for thoughts guys!
     
  9. randy448

    randy448 LawnSite Member
    Posts: 39

    Put it on a charger later on. A dead battery will not charge very good off the alternator, he may drive 10 minutes and stop and not be able to get started again. Seen this alot at co. I worked for years ago. Jump it go to job site and 3:00 PM dead again.
     
  10. Albemarle Lawn

    Albemarle Lawn LawnSite Bronze Member
    Posts: 1,544

    A proper jump is a parallel circuit: voltage stays in 14v range.
     

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